Known is an inverted pendulum type vehicle or an omni-directional vehicle comprising a pair of drive assemblies individually actuated by electric motors and a main wheel held between the drive assemblies and frictionally driven by the drive assemblies. See WO2008132779A1 (US20100096905A1) (patent document 1) for instance. Each drive assembly comprises a drive disk coaxially opposing the drive disk of the other drive assembly and a plurality of drive rollers obliquely arranged along the circumference of the drive disk at a regular interval so as to be individually rotatable. The main wheel comprises a ring-shaped annular member rotatably supported by a frame around a central axial line thereof and a plurality of driven rollers arranged along the circumference of the annular member so as to be rotatable around the respective tangential lines. As the drive disks are turned by the electric motors, the driven rollers are frictionally driven by the drive rollers. When the drive rollers are turned around the tangential directions of the main wheel, the vehicle is driven in a lateral direction. When the main wheel is turned around the central axial line thereof, the vehicle is driven in a fore and aft direction. The direction of motion of the vehicle can be selected as desired by suitably adjusting the difference between the rotational speeds of the two drive disks.
The vehicles of this type are suited to have a small footprint (area of the image of the vehicle projected on the ground surface), and this enables the vehicle to travel in narrow spaces. Japanese patent laid open publication No. 2006-282160 (patent document 2) discloses such an inverted pendulum type vehicle comprising a robot main body consisting of a spherical wheel and an omni-directional drive unit for rolling the spherical wheel in a desired direction, and a control unit for maintaining the robot main body in an upright posture under an inverted pendulum control.
In this vehicle, the robot main body further includes a casing receiving a battery, a control computer, motor drivers, a gyro sensors and other control components, and a protective cover attached to a lower part of the casing and covers the omni-directional drive unit. When this structure is applied to an inverted pendulum vehicle using a main wheel having a relatively small width, the protective cover may have a small width, but the casing is required to have a large width that does not match the narrow width of the protective cover. Therefore, the vehicle is prevented from having a small footprint.
Furthermore, the amount of the wiring connecting various parts of the vehicle is desired to be minimized for a compact and small foot print design of the vehicle. Also, the wiring is required to be accessible for assembly and maintenance purposes.
In an inverted pendulum control of a vehicle, it is important to detect the inclination angle of the vehicle without time delay. An inclination angle typically consists of a gyro sensor. However, when the sensor is provided in a part of the vehicle remote from the gravitational center of the vehicle, the motion of the vehicle is given as a combination of the motion of the gravitational center of the vehicle and the motion of the mounting point of the sensor with respect to the gravitational sensor. Therefore, the computational load can be minimized if the inclination sensor (gyro sensor) is mounted on the gravitational center of the vehicle.
An inverted pendulum type vehicle typically includes a rechargeable batter, a drive unit and an electric unit for controlling the supply of electric power from the battery to the drive unit, and these form three major assemblies that account for a large part of the weight and bulk of the vehicle. It is therefore important to arrange them that the vehicle may be compactly designed, and the accessibility of various components may be ensured.